(1) Field of the Invention
This invention relates to a method of forming a film of boron carbide on a substrate, and more particularly the invention relates to a method of manufacturing a composite material with a film of boron carbide that is effectively capable of being used as an abrasion-resisting material, a sliding-material, a heat-resisting tile in a rocket and the like, and a control material, a shield material, etc. in a nuclear reactor and so on.
(2) Related Art Statement
Boron carbide has a very high melting point, so it has good heat-resistance. It has also chemical stability, so it has good oxidation-resistance. Moreover it has good mechanical strength such as abrasion-resistance, and hardness, and high neutron absorbability.
Materials covered with boron carbide, therefore, have been conventionally used as a abrasion-resisting material, a sliding material such as for inner surfaces of sandblasting nozzles and a crushing machine, a heat-resisting tile in rocket, and control-material and a shield-material in the nuclear reactor.
The material is generally covered with boron carbide by CVD, plasma spraying or the like.
When the boron carbide film is, however, formed on the substrate material by the above plasma spraying, the film is disadvantageously cracked or peeled off.
To solve the above problems, Japanese patent Laid-open No. 5-339079 shows a method in which a surface of a carbonaceous material as a substrate is converted into boron carbide, powdery boron carbide is put on a converted layer of boron carbide or a layer of boron carbide is formed on a surface of the substrate by CVD or the like, and finally the resulting substrate is hot-pressed to form a dense boron carbide film.
Moreover Japanese patent Laid-open No. 7-33567 discloses a method in which secondary quasi-particles with 3.about.50 .mu.m in diameter are prepared by cohering fine particles of nitride or carbide with 0.01.about.1 .mu.m in diameter, and coated onto a surface of a carbonaceous material as a substrate by plasma spraying, and at least one layer of a metal, an alloy, an oxide-based ceramics or a non-oxide type ceramics is laminated upon the resulting substrate by spraying.
However, the above methods cannot sufficiently prevent cracking and peeling-off of the boron carbide film coated on the substrate, and this tendency becomes conspicuous particularly under a high humidity condition. So the boron carbide film cannot have the characteristics such as heat-resistance and abrasion-resistance which are unique to boron carbide.